Inflatable variable-bandwidth antenna



March 30, 1965 Filed June 14, 1962 C. D. TIPTON @EZAPCE'E HUOWE INFLATABLE VARIABLE-BANDWIDTH ANTENNA 2 Sheets-Sheet 1 INVENTOR. CHARLES 0. TIPTON MMMQ AGENTS March 30, 1965 c. D. TIPTON 3,176,302

INFLATABLE VARIABLEBANDWIDTH ANTENNA Filed June 14, 1962 2 Sheets-Sheet 2 INVENTOR. CHARLES 0. T/PTO/V BY mm M QM AGENTS United States Patent Iowa Filed June 14, 1962, Ser. No. 202,430 2 Claims. (Cl. 343-872) This invention pertains to inflatable antenna structures and particularly to structures in which the curvature of their surfaces may be varied to change the beam width of radiated energy.

An inflatable antenna with a fixed beam width is described in US. Patent No. 2,814,038, issued to C. J. Miller on November 19, 1957. Such an antenna system having a large inflatable reflector is light weight and is readily disassembled and folded for transportation. The utility of the antenna can be improved according to the present invention by providing quick change in beam width. This improvement is particularly advantageous during communication with or tracking of approaching aircraft. While the aircraft is far away, a narrow beam width is desirable and often necessary to provide the gain required for communicating with the aircraft. For near aircraft, a broad beam width permits easy tracking while the aircrafts direction of travel departs quite widely from the direction of a direct line between the antenna and the aircraft. Also, when the beam width is broad, communication may be maintained with a plurality of near aircraft.

The improvement of this invention comprises a flexible diaphragm having conductive strips stretched in a plane extending across an inflatable housing and means for establishing differential in pressure on opposite sides of said diaphragm to change the surface defined by said strips from a plane surface to a desired curved surface.

An object of this invention is to provide a variable beam-width antenna.

Another object is to provide a variable beam-width antenna of lightweight construction that can be readily disassembled for transportation.

The following description and the appended claims can be more readily understood with reference to the accompanying drawings in which:

FIG. 1 is an obique view of an inflatable antenna structure with portions cut away to show construction of its inflatable housing and its reflector;

FIG. 2 is a cross-sectional view of the inflatable housing and reflector with the reflector positioned for broadbeam operation; and

FIG. 3 is a cross-sectional view of the housing and reflector with the reflector positioned for narrow-beam operation.

With reference to FIG. 1, the antenna structure is secured to base 11 that is rotatably mounted to a fixed mounting base 12. An envelope or outer housing 13 is sealed to the base 11 and supported by an inner tubular ring 14 that is also sealed to the base 11. A high-pressure blower 15 has an outlet communicating with the enclosed cavity of the ring 14 for maintaining pressure in the ring. When under pressure the ring presses out wardly against the inside wall of the housing 13 to maintain its periphery substantially annular according to the pattern of the housing. Additional rigidity is supplied by the folding mechanical arms 16 that are secured to the base 11 and enclose a portion of the outer periphery of the envelope that is supported by the internally mounted ring 14. The pattern of the envelope 13 determines that the rear wall is parabolic when the envelope is inflated.

A flexible diaphragm 17 comprises nonconductive fabric 18 and parallel, spaced conductive strips 19. It

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is stretched across the supporting ring 14 to divide the outer envelope 13 into front and rear compartments. When the pressure in one compartment is the same as that in the other, the conductive strips 19 are retained on a plane circuit as shown in FIG. 2 by elastic mounting portions 20 that secure the strips to the supporting ring 14.

A low-pressure blower 21 for inflating the antenna envelope is mounted to base 11 and operated by a source of power, not shown. The outlet of the blower 21 communicates through a T-valve 22, its outlet ducts 23 and 24 to the rear and front compartments respectively of the envelope 13. By operating the T-valve 22, the air flow from outlet 23 can be reduced or shut off so as to decrease the pressure in the rear compartment relative to that of the front compartment.

A suitable material for fabricating the envelope 13 and the diaphragm 17 is a polyester fiber impregnated with material having qualities of rubber. Such a material is made of a fiber sold under the trade name Dacron impregnated by a rubber substitute sold under the trade name Neoprene. The deflective conductive strips 19 are made of a silver-thread mesh material and their ends are made of an elastic rubber substitute that is bonded to the ends of the conductive strips.

Signal energy for illuminating the reflector that comprises conductive strips 19 is applied through a coaxial cable 25 to a horn antenna 26. The horn antenna is positioned at the apex of the parabola formed by the reflector when the diaphragm 17 is pressed backward against the rear wall of the envelope 13.

As described above, when the valve 22 is adjusted so that the pressure is the same in the front and the rear compartments of the envelope 13, the conductive strips 19 are positioned in a plane. The reflector then functions as a mirror to provide an image of the field pattern of the horn. The pattern of the horn is essentially dependent upon the angle subtended for illuminating the greater portion of the surface of the reflector. For example, the angle subtended by the cone of radiation might be 70 degrees. When communication is desired with a distant station, valve 22 is operated to close the outlet 23 that sup plies air to the rear compartment. The air that is supplied to the front compartment through outlet 24 presses the diaphragm 17 rearwardly against the parabolic rear wall of the envelope 13. For a signal that has a frequency from 200 to 300 megacycles, the beam width is then reduced from approximately 70 degrees when the reflector is in a plane to approximately 20 degrees.

Although this invention has been described with respect to a particular embodiment thereof, it is not to be so limited, as changes and modifications may be made therein which are within the spirit and scope of the invention as defined by the appended claims.

What is claimed is:

1. In an antenna system having an inflatable housing, a variable beam-width reflector comprising, a flexible diaphragm having spaced elastic flexible parallel strips, each of said strips having conductive portions, the ends of said strips being secured to the periphery of the housing of said inflatable antenna to normally position said strips in a plane within said housing, and means for providing a pressure differential on opposite sides of said diaphragm whereby said strips are positioned on a curved surface for changing the beam width of said antenna system.

2. An inflatable variable bandwith antenna comprising, an inflatable housing have flexible nonconductive front and back walls, a tubular. flexible ring within said housing inflatable to relatively high pressure for providing a firm diameter common to said front and back wall, said back wall when said housing is inflated being parabolic, a

3 4 flexible diaphragm having its periphery sealed to said ring References Cited by the Examiner for dividing said housing into separate front and rear in- UNITED STATES PATENTS flatable compartments, said diaphragm having parallel reflector strips with elastic ends, said elastic ends being 504,890 2 Ohmart secured to said ring to provide required tension for posi- 5 1,855,155 Sampson 343 908 X tioning said strips that are attached to said diaphragm in 2814038 11/57 Miner a plane across said housing while the pressure differential 2952189 9/60 pales 88 73 between said compartments is small, and means for in- 3001196 9/61 Mcnmy e 31 3439 15 creasing the pressure in said front compartment while 3047860 7/62 Swallow et a1 343 915 reducing the pressure in said rear compartment until said 10 diaphragm is pressed against said parabolic back wall. HERMAN KARL SAALBACH Primary Examiner 

1. IN AN ANTENNA SYSTEM HAVING AN INFLATABLE HOUSING, A VARIABLE BEAM-WIDTH REFLECTOR COMPRISING, A FLEXIBLE DIAPHRAGM HAVING SPACED ELASTIC FLEXIBLE PARALEL STRIPS, EACH OF SAID STRIPS HAVING CONDUCTIVE PORTIONS, THE END OF SAID STRIPS BEING SECURED TO THE PERIPHERY OF THE HOUSING OF SAID INFLATABLE ANTENNA TO NORMALLY POSITION SAID STRIPS IN A PLANE WITHIN SAID HOUSING, AND MEANS FOR PROVIDING A PRESSURE DIFFENTIAL ON OPPOSITE SIDES OF SAID DIAPHRAGM 